package day6;

import java.util.Scanner;


//不要二
public class oj2 {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int w = scan.nextInt();
        int h = scan.nextInt();
        int[][] array = new int[w][h];
        int count = 0;
        for(int i = 0; i < w; i++) {
            for(int j = 0; j < h; j++) {
                if(array[i][j] == 0) {
                    count++;
                    if(i + 2 < w) {
                        array[i + 2][j] = 1;
                    }
                    if(j + 2 < h) {
                        array[i][j + 2] = 1;
                    }
                }
            }
        }
        System.out.println(count);
    }
}
